1. Field of the Invention
The present invention relates generally to a viscous fluid drive device. In particular, the present invention is concerned with an improved clutch plate of a viscous fluid fan clutch for a vehicle.
2. Description of the Related Art
The use of a viscous fluid clutch for controlling the rotation of an engine cooling fan for a vehicle is very well-known. A multi-bladed fan is removably secured to a fan clutch installed between an accessory pulley (typically the water pump pulley) of a vehicle engine and a radiator. The clutch drives the fan at high speeds close to input speed when cooling is required and permits the fan to rotate at low speeds when cooling is not required. Thermostatic control of the fan through the clutch reduces airflow noise caused by fan rotation and the load on an engine, resulting in horsepower gain and improved fuel economy.
Generally, a clutch plate, housed within the clutch assembly, having lands and grooves is mated to a housing having complementary lands and grooves. An internally-contained pump plate separates a working chamber from a reservoir. Gates in the pump plate permit selective flow of a viscous fluid from the reservoir to the working chamber and into a shear zone between the lands and grooves of the housing and clutch plate. Fluid shear in the lands and grooves transfers input torque from the clutch plate to drive the housing and attached fan.
When cooling is not required, gates in the pump plate are closed and the fluid in the shear zone is pumped into the receiving chamber. Orifices in the pump plate permit passage of the fluid from the working chamber to the reservoir. The removal of a majority of the fluid reduces the shear between the clutch plate and the housing, thereby substantially reducing the rotation of the housing and attached fan.
U.S. Pat. No. 4,741,421, issued May 3, 1988 and assigned to the assignee of the present invention, discloses a sealing ring operatively disposed between facing surfaces of a clutch plate and pump plate in a viscous fluid fan clutch. The sealing ring positively diverts fluid flow into axial flow passages formed in the clutch plate, thereby ensuring that all viscous fluid is subjected to shear by the interdigitated lands, which form a shear zone. The sealing ring improves fluid fill and clutch drive time.
It is desirable to produce a fan clutch wherein a sealing ring is not required to control fluid flow.